To test the hypothesis that episodic hypoglycemia increases the frequency of subsequent iatrogenic hypoglycemia in the clinical setting in patients with IDDM, the frequency of asymptomatic (biochemical) symptomatic and severe iatrogenic hypoglycemia is determined in patients with IDDM during a 4 week period of clamped hypoglycemia (approx. 2.8 mmol/L x 2h twice weekly) and during a 4 week period of otherwise identical clamped hypoglycemia (approx. 8.3 mmol/L x 2h twice weekly.)